Turbo Decoding in a Rayleigh Fading Channel with Estimated Channel State Information

In this paper, a new method to estimate the parameter for turbo decoding using the maximum a posteriori probability (MAP) algorithm is proposed for a turbo code in a Rayleigh fading channel with imperfect channel estimation. This parameter is called the channel reliability factor and is related with the channel SNR. For channel estimation, pilot symbol assisted modulation (PSAM) is used and the channel reliability factor for PSAM is derived. It is shown that the proposed estimator for the channel reliability factor does not degrade the error performance of turbo codes, compared with the case in which the channel reliability factor is exactly known to the decoder. It is also shown that the performance gain of Log-MAP algorithm over Max-Log-MAP algorithm can be maintained by using the correct channel reliability factor, irrespective of the channel estimation error.